Soil water characteristic (SWC) curve is a fundamental soil property. However, its measurement is expensive and time-consuming. Therefore, many physical and mathematical methods were derived for its estimation instead of its measurement. One of these methods is Arya et al. (1999) model which estimates SWC curve from soil particle-size data assuming a constant void ratio. In this paper, SWC curves of thirty Iranian soils were estimated by using the model of Arya et al. (1999) based on local void ratio, and then the proposed model was validated for eighteen different soils by using a new derived equation for considering local void ratio. The results indicated that the local void ratio approach improved the estimation of SWC curve.
Key words: Soil water characteristic curve, soil-particle size distribution curve, local void ratio, logistic, linear, scaling factor.
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